Project summary Global Polio Eradication Initiative started by WHO in 1988. It resulted in more than 99% reduction of polio morbidity worldwide, but missed the original eradication deadline in year 2000. In the past 15 years its progress was interrupted by a number of significant setbacks (1, 2). It has become increasingly clear that the suboptimal properties of existing anti-polio vaccines are one of the major challenges in the campaign. Currently the efforts are focused on incremental improvements of the two types of anti-polio vaccines available - inactivated vaccine (IPV) and oral live attenuated vaccine (OPV). Yet both of types of vaccines have intrinsic flaws that jeopardize achieving the ultimate eradication goal. Production and administration of IPV is prohibitively expensive in low-income countries. In addition, IPV does not induce adequate mucosal immunity necessary to stop the virus transmission. Despite its impressive success, the use of OPV has become a major liability because of the genetic instability of vaccine strains that regain pathogenicity. An ideal vaccine should combine economic and protective efficacy of OPV with the safety of IPV. We propose to develop a live vectored vaccine as a novel approach to producing safe and effective anti- poliovirus vaccine. Newcastle disease virus (NDV)-based vectored vaccines have shown encouraging results for vaccinations against many human pathogens. Most importantly NDV-based vaccines were shown to induce strong mucosal immunity (8-12, 17). In this exploratory project, we propose to engineer recombinant NDVs co- expressing the precursor of poliovirus capsid proteins P1 and the protease 3CD responsible for its processing. We anticipate that co-expression of these poliovirus proteins in cells infected with recombinant NDV vector will result in robust generation of poliovirus-like particles as it was observed in many other P1 and 3CD co- expression systems. Picornavirus-like particles are known to be antigenically similar to the normal virions and be able to induce protective immune responses (4, 7, 22, 40, 45). To enhance the immunogenicity and protective efficacy of our NDV vectored vaccine, we aim to optimize the co-expression levels of the capsid protein P1 and protease 3CD by flanking the polio transcription cassettes with untranslated regions (UTRs) of NDV and/or internal ribosome entry site (IRES) elements in the transcriptional unit. The novel recombinant NDV-based vaccine will be evaluated against existing IPV vaccine in a murine model of poliomyelitis (31). Humoral, mucosal, and cellular immunity will be assessed to identify the most promising vector design. Determination of virus load in tissue samples, virus shedding, and clinical signs will be used as the criteria to evaluate the protective efficacy of our vaccines. As a rule, production of live vaccines is less costly than inactivated vaccines, which may provide yet another advantage of the proposed vaccine over conventional or a new-generation IPV. We expect that this study will allow us to evaluate whether live NDV vectored vaccines can be a better strategy to develop economically affordable, absolutely safe, and highly effective anti-poliovirus vaccine.